1. Field of the invention
The present invention relates to an ink-supplied wire dot matrix printer head having wires supplied with ink at their distal end faces and movable against a sheet of print paper for transferring ink to the sheet in the form of dots to record a character, a figure, a graphic image or the like on the sheet, and more particularly to the construction of an ink tank and an ink guide for guiding ink from the ink tank to the distal end faces of the wires.
2. Description of the Prior Art
Ink supply systems for a wire dot matrix printer are known in which no ink ribbon is used, but ink is supplied from an ink tank to the distal ends of the wire and transferred from the wires directly to a sheet of print paper. One known ink guide mechanism for such an ink supply system is disclosed in U.S. Pat. No. 4,194,846 and comprises a porous member capable of absorbing ink and for guiding ink from an ink tank with wires contacting the porous member. The porous member contains fine holes with their sizes or diameters varying within a certain range, with the result that the ink absorbing capability varies from porous member to porous member, and excessive and insufficient quantities of ink tend to be supplied to the distal ends of the wire. The quantities of ink retained in the vicinity of the distal ends of the wires widely differ, and the porous member is liable to vary in dimensions or be deformed due to coaction with the sides of the wires. Therefore, the ink densities of formed dots are irregular.
As shown schematically in FIG. 10, the ink tank frequently tends to trap air pockets in the ink-impregnated member. When ambient temperature rises or atmospheric pressure is lowered under such a condition, air communicating directly with the air hole expands and is discharged out of the air hole as indicated by the arrows A without applying any pressure on impregnated ink, whereas the completely trapped air is expanded as indicated by the arrows B while moving the ink surrounding it. When such air pocket reaches the ink supply port, an undesired ink outflow occurs. This causes a smear or ink spot on a sheet of print paper, or ink finds its way.
Accordingly, it is desirable to provide an ink-supplied wire dot matrix printer head which overcomes these problems associated with the prior art.